Initially, detergents used in industrial laundries were formulations of dry products or powders. The industry trend (over the past five years) has been moving toward formulated liquid products since these offer handling advantages versus dry products. Liquid detergents can be automatically dosed to washing machines using pumping equipment which reduces potential errors in dispensing, reduces labor, and allows automatic tracking of chemical usage.
Liquid detergents are primarily liquid surfactant blends. The primary function of surfactant is to wet surfaces and emulsify soils. These detergents can incorporate other components such as degreasers, brighteners, viscosity modifiers, dyes, and the like. Alkaline builders, sequestering agents, bleaches and finishing chemicals such as starches, softeners, and sours can be added separately. One particularly useful bleach is hydrogen peroxide. Compared to chlorine bleach, it is more suitable for the environment since it decomposes into water and oxygen.
Hydrogen peroxide is typically available in an aqueous solution. When the surfactant system contains a significant amount of hydrophobic surfactant (i.e., has a hydrophilic-lipophilic balance (HLB) of less than about 11-12), the addition of aqueous components causes the surfactant blend to approach the gel phase which increases viscosity. This interferes with the detergent feed system causing delivery errors and increased delivery times. Gels also require longer dissolution times once inside the washer. Viscosity may be modified by adding various hydrotropes. However, solvated hydrotopes tend to lower the flashpoint of the detergent.
Accordingly, it is an object of the present invention to incorporate aqueous components into a liquid laundry detergent having a surfactant system which would normally not accept aqueous components and preferably to incorporate an aqueous solution of hydrogen peroxide into such a surfactant system. This is accomplished by adding to the surfactant system N-methyl pyrrolidone (NMP) in an amount effective to permit addition of at least about 15% by weight of an aqueous component and again preferably an aqueous solution of hydrogen peroxide. Generally the detergent system will contain a water-insoluble surfactant and have an HLB of 9 to about 12.